(1) Field of the Invention
The present invention pertains to improvements to hermetic sealing apparatus of the type disclosed in U.S. Pat. No. 4,295,653, herein incorporated by reference, wherein the sealing apparatus incorporates a sensitive monitoring system that detects slight leaks of sealing liquid from the apparatus.
(2) Description of the Related Art
In working with hazardous substances, for example toxic chemicals or radioactive substances, enclosures containing these substances under pressure are often required to have actuator rods extending through the walls of the enclosures to operate mechanisms contained in the enclosures. For example, in conveying hazardous fluids through pipelines, it is often necessary that there be an actuator rod extending through a wall of the pressure vessel to operate a valve in the vessel.
Reciprocating movement of the actuator rod through an opening in the vessel wall would selectively open and close the valve controlling the flow of the hazardous substance through the enclosure. In another example, the actuator rod may extend through an opening in an enclosure containing a hazardous substance to operate a control button also contained in the enclosure. In this example, reciprocating movement of the rod through the opening of the enclosure selectively presses downward on the control button or releases upward from the control button. In each of these examples and in others where the enclosure contains hazardous and perhaps lethal substances, it is extremely important that there be no leakage of the substances to the environment exterior to the enclosure. Therefore, it is necessary that the mounting of the actuator rod to the enclosure wall permitting reciprocating movement of the rod through an opening in the wall be hermetically sealed in a manner that reliably prevents leakage of any of the hazardous substance from the enclosure to the exterior environment.
A reliable hermetic seal that permits movement of an actuator rod through an opening in an enclosure containing a substance under pressure while preventing leakage of the substance from the enclosure to the exterior environment is disclosed in U.S. Pat. No. 4,295,653. The hermetic sealing apparatus disclosed in this patent employs a pair of concentric bellows and a pressure compensating sealing liquid. The principle behind the operation of this sealing apparatus was to minimize the pressure difference across the pair of sealing bellows by filling an area of the valve housing behind the sealing bellows from the hazardous substances with the sealing liquid. Within the chamber of the valve housing the pair of concentric bellows are attached to a free floating piston that is free to slide upward and downward over the actuator rod extending through the valve housing and through the hole in the enclosure into the interior of the enclosure containing the hazardous substance. The inner bellows of the pair is also attached to the actuator rod and the outer bellows is attached to an inside wall of the valve housing. A conventional packing seal is employed around the actuator rod as it exits the valve housing to prevent the leakage of the sealing liquid from the interior of the valve housing.
The concentric bellows and the free floating piston act as a flexible barrier between the sealing liquid contained within the valve housing and the hazardous substances contained in the enclosure that enters the valve housing on the opposite side of the bellows/piston assembly from the sealing liquid. In the design of this sealing apparatus, the bellows/piston assembly is designed to move freely over a portion of the actuator rod's length as the actuator rod is moved through the enclosure opening to operate a device contained in the enclosure with the hazardous substance. The bellows/piston assembly thereby maintains the volume of sealing fluid in the valve housing constant. As the actuator rod is moved downward through the enclosure opening and into the enclosure interior volume the bellows/piston assembly moves upward over the rod. As the actuator rod moves upward through the enclosure opening from the interior volume of the enclosure the piston/bellows assembly moves downward over the rod. Throughout all movements of the actuator rod and the bellows/piston assembly the pressure of the hazardous substances acting on one side of the bellows/piston assembly is transferred to the sealing liquid contained on the opposite side of the bellows/piston assembly.
The packing seal surrounding the actuator rod as it exits the valve housing is exposed to the sealing liquid contained in the housing. The sealing liquid employed may be a lubricant which facilitates reciprocating movement of the actuator rod through the packing seal and serves to enhance the seal of the packing around the rod. Any minute seepage of the sealing liquid through the packing seal could be replenished as needed through a valve replacement port. Should the packing seal leak continuously, means could be provided to monitor the leakage, for example a sight glass, which would provide an indication of when replenishment of the sealing liquid would be necessary.